Carpet bombing, rain of lazers, city under nuclear fire.
One minute in game is one wave of enemies.
The difficulty curve is something like this :

Wave 1 : "hmm, this game is for babies"
Wave 5 : "this game is not so easy"
Wave 10 : "I WILL NOT MAKE IT, HEELP"

The world record is actually 22 waves by :
?★★★EccentricRhombus398 ★★★?

Second place is Vylexia? with 17 waves.
Third place is SirQuboid? with 16 waves.

How to play :
Shoot on every thing in the sky.
Use your finger and tap on the screen to use your loaded weapon.
Weapons with full auto can be used by holding finger on screen.
when you shoot an enemy, a bonus can appear.
It can be a weapon, shield or life, don't shoot it if you need it.
If you reach 999 gold points, you unlock a special weapon.
You can do checkpoints at end of waves with your gold points.
Ads are not intrusive.